IRREGULAR POLLEN EXINE2 Encodes a GDSL Lipase Essential for Male Fertility in Maize.

Anther cuticle and pollen exine are two physical barriers protecting plant reproductive cells against environmental stresses; defects in either often cause male sterility. Here, we report the characterization of a male-sterile mutant irregular pollen exine2 (ipe2) of maize (Zea mays), which displays shrunken anthers and no starch accumulation in mature pollen grains. We cloned the causal gene IPE2 and confirmed its role in male fertility in maize with a set of complementary experiments. IPE2 is specifically expressed in maize developing anthers during stages 8 to 9 and encodes an endoplasmic-reticulum-localized GDSL lipase. Dysfunction of IPE2 resulted in delayed degeneration of tapetum and middle layer, leading to defective formation of anther cuticle and pollen exine, and complete male sterility. Aliphatic metabolism was greatly altered, with the contents of lipid constituents, especially C16/C18 fatty acids and their derivatives, significantly reduced in ipe2 developing anthers. Our study elucidates GDSL function in anther and pollen development and provides a promising genetic resource for breeding hybrid maize.